The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. Examples of implantable medical devices include neurostimulators, infusion devices, pacemakers, defibrillators, diagnostic recorders, and cochlear implants. While such devices may vary in their mechanisms of therapeutic or diagnostic action or their therapeutic or diagnostic target, they do share common concerns or design issues.
For example, it is desirable to minimize the rate of infection associated with implantation of medical devices; as such infections are a serious health and economic concern. Today, infections associated with implanted medical devices are not very common due to care and precautions taken during surgical implantation of the devices. However, when infection associated with an implanted medical device does occur, explanting the device is often the only appropriate course of action.
In addition, it is desirable to design such devices such that they fit comfortably within a patient and provide therapy for an extended period of time. However, some medical devices provide therapies with significant power demands, placing limits on how small the size of power supply may be. To reduce the size of such implantable medical devices and extend their therapeutic life, rechargeable power supplies, which can be smaller than their non-rechargeable counterparts, may be employed. Recharging of such devices typically includes applying to a recharge coil of the implanted device a transcutaneous recharge signal produced by a primary coil. However, the recharge process causes heating of the implanted device and surrounding patient tissue, particularly in proximity to the secondary recharge coil. Excessive heating may result in damage to the patient tissue. Accordingly, the amount of energy applied is controlled over time to minimize heating.
While it may be desirable to minimize the amount of heat allowed to generate during a recharge process to avoid damage to tissue of the patient, it may be desirable to allow for heating of the device when an infection is present to improve clearance of the infection.